add information about linkhandler

docs/02_Concept_of_LinkHandler.md

@@ -1 +1,50 @@
 # Concept of LinkHandler
+
+LinkHandler represent Links to resources like videos, search requests, channels, etc.
+The idea behind them is that a video can have multiple links pointig to it, but it has
+one unique id that represents it, like this example:
+
+[oHg5SJYRHA0](https://www.youtube.com/watch?v=oHg5SJYRHA0) can be represented as:
+
+- [https://www.youtube.com/watch?v=oHg5SJYRHA0 (default url for youtube)](https://www.youtube.com/watch?v=oHg5SJYRHA0)
+- [https://youtu.be/oHg5SJYRHA0](https://www.youtube.com/watch?v=oHg5SJYRHA0)
+- [https://m.youtube.com/watch?v=oHg5SJYRHA0](https://www.youtube.com/watch?v=oHg5SJYRHA0)
+
+### Importand notes about LinkHandler: 
+- A simple `LinkHandler` will contain the default URL, the ID and the original url.
+- `LinkHandler` are ReadOnly
+- LinkHandler are also used to determine which part of the extractor can handle a certain link.
+- In order to get one you must either call [fromUrl()](https://teamnewpipe.github.io/NewPipeExtractor/javadoc/org/schabi/newpipe/extractor/linkhandler/LinkHandlerFactory.html#fromUrl-java.lang.String-) or [fromId()](https://teamnewpipe.github.io/NewPipeExtractor/javadoc/org/schabi/newpipe/extractor/linkhandler/LinkHandlerFactory.html#fromId-java.lang.String-) of the the coresponding `LinkHandlerFactory`.
+- Every type of Type of Resource has its own LinkHandlerFactory. Eg. YoutubeStreamLinkHandler, YoutubeChannelLinkHandler, etc.
+
+### Usage
+
+So the typical Usage for getting a LinkHandler would look like this.
+```java
+LinkHandlerFactory myLinkHandlerFactory = new MyStreamLinkHandlerFactory();
+LinkHandler myVideo = myLinkHandlerFactory.fromUrl("https://my.service.com/the_video");
+```
+
+### Implementation
+
+In order to Use LinkHandler for your service you must override the apropriate LinkHandlerFactory. eg:
+
+```java
+class MyStreamLinkHandlerFactory extends LinkHandlerFactory {
+    
+    @Override
+    public String getId(String url) throws ParsingException {
+        // Return the ID based on the url.
+    }
+
+    @Override
+    public String getUrl(String id) throws ParsingException {
+        // Return the url based on the id given.
+    }
+
+    @Override
+    public boolean onAcceptUrl(String url) throws ParsingException {
+        // Return true if this LinkHanlderFactory can handle this type of link
+    }
+}
+```

mkdocs.yml

@@ -2,3 +2,5 @@ site_name: NewPipe Documentation
 theme:
     name: readthedocs
     custom_dir: theme 
+markdown_extensions:
+   - fenced_code